The fossil has been identified as the knucklebone of a Plateosaurus, a massive, plant-munching dino that lived some 200 million years ago.

The discovery was made about 87 miles (140 kilometers) west of Norway in the Snorre oil field. Geologists Morten Bergan and Johan Petter Nystuen spotted a bone-like fragment in a drill corea long cylinder of rock from an oil exploration well.

A dinosaur fossil has never been found so far underground, says Jørn Hurum of the Natural History Museum, University of Oslo.

"It's a very small piece of boneabout three centimeters [1.2 inches]," he said.

Hurum, as Norway's only dinosaur researcher, had the difficult task of trying to identify the find. He took a slice from the fossil just a few thousandth of a millimeter thick for microscopic examination.

German Fossils

While the examination confirmed the remains as a dinosaur's, it wasn't until Hurum compared the fossil with specimens in Germany that he made the link.

Plateosaurus was a giant, long-necked plant-eater that grew 30 feet (9.1 meters) long and weighed as much as four tons (4.1 metric tons). An early dinosaur, it is known to have lived in modern-day Europe and Greenland between 210 and 195 million years ago.

"Plateosaurs have a special kind of bone structure which is not seen in any other dinosaurs from this period," Hurum said. "They were one of the most common dinosaurs. Hundreds of skeletons have been found in Europe."